Air Lift Pump – Working Principle, Parts and Working

Air lift pump is a device that is used to lift water from a well or a sump with the use of compressed air. This pump is also called a mammoth pump.
Airlift pumps have been used since the beginning of the 20th century.
The first airlift pump was invented by the German Engineer Carl Emanuel Loscher in 1797.
Air Lift Pumps are generally found in agricultural lands.

They are simple devices in which liquid enters from one end and a mixture of air and liquid discharges from the other end.
Air is injected near the inlet. Almost without exceptions, the riser section of airlift pumps has been vertical pipes with circular cross-sections.

Airlift pumps are generally used when the maintenance needs to be kept to an absolute minimum. But this pump is not 100% maintenance free as equipments are needed to feed air into the pump which needs maintenance.

Different Symbols in the diagram:-
h – distance between the nozzle tip and static water level.
H – distance between the nozzle tip and center point of the end of the delivery pipe
where the water gets discharged.
H – h (difference of H and h) – Useful Liftnull

Working Principle:-

In air lift pump, the compressed air is mixed with water. We know that the density of water is much more than the density of air.
By buoyancy, the air which has a lower density than the liquid rises quickly.
By fluid pressure, the liquid is taken in the ascendant air flow and moves in the same direction as the air.

Air is fed into the bottom of the riser pump and this air combines with water and form froth. As the water mixes with air, the density of water decreases because of the density of air and water mixture is less than the density of water.
So the air and water mixture which is also called froth has much less density than water. So main principle of air lift pump is density difference between air and water mixture and water.

The efficiency of an airlift pump depends on two things:
1) The submerged length (Hs) in relation to geodetic head (Hgeo).
2) Air speed through the fluid and the velocity to the medium through the pump. The greater the difference between the respective velocities of the fluid and air, the lower the overall efficiency of the pump.

For these pumps, the air injector system is in the form of an air jacket in which several holes are drilled radially through the pipe and air is supplied to them from a surrounding manifold.

For good results,
H – h < h
The ratio h / H-h is always between 4 and 8.

Parts of Air Lift Pump:-

1) Air compressor:
Air compressor is used to compress the air and supply the compressed air to air pipeline. The compressed air is usually produced by an engine-driven air compressor, but windmill-powered air compressors are also used.

2) Air pipeline:
The compressed air is sent to the delivery pipe using this air pipeline. The top end of this pipe is connected to the air compressor while the air nozzle is attached at the bottom end.

3) Delivery Pipe:
This pipe is used to lift water from the well. The water and air mixture rise above using this pipe. Both ends of the delivery pipe are open. The bottom end of this pipe is immersed in water through which water is lifted.

Working:-

At first, the compressed air is passed through the air pipeline to the air nozzle with the help of an air compressor.
The air nozzles are installed as per requirement, it can be one or more.
The air nozzle is located at the very bottom of the delivery pipe. The position of the delivery pipe is fixed in the well and through this pipe, water is lifted from the well.
When air enters the delivery pipe from the air nozzle, the air mixes with the water present in the delivery pipe. The density of air and water mixture will be very low if it is compared with pure water present in a deep well.
The density of pure water is high and the density of the air-water mixture is low and due to the difference in this density, it will be possible that a small column of pure water will be able to balance the large column of air and water mixture and for this reason, the mixture of air and water will be discharged through the delivery pipe.
As soon as the pressure in the delivery pipe of height H becomes less than the pressure due to the height of water column h in the outlet of the delivery pipe, the water begins rising in the delivery pipe above the level of water outside the delivery pipe.
Another reason for the rise of water is that water in the delivery pipe is lighter than water outside delivery pipe.
This discharge lasts as long as the supply of compressed air continues through the air compressor.

Advantages of Air Lift Pump:-

1) The air lift pump does not have any moving parts below the water level and hence there are no chances of suspended solid particles damaging the pump.
2) This pump can raise water through a borehole of a given diameter than any other pump.
3) Less maintenance is required.
4) This pump can handle sand, mud and gritty water too.
5) The pump is very suitable when decompressed air is available.

Disadvantages of Air Lift Pump:-

1) Conventional airlift pumps have a flow rate that is very limited.
2) Efficiency is very nearly 20 to 30% when compared to the expenditure of energy in compressing air.
3) It can not lift up the water if the level of water goes down below the limit.
4) The suction is limited.

Applications:

1) Airlift pumps are often used in deep dirty wells where conventional pump usage is difficult as sand would quickly abrade mechanical parts.
2) These pumps are also used to collect fauna samples from sediment.
3) Sometimes used in wastewater treatment plants if a small head is required.
4) It is also used in deep-sea mining.
5) Also used in the recovery of archeological artifacts and many more.
6) Sometimes used in an aquarium to pump water to filter.

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